Rib scaling and the stability of coal pillars

ABSTRACT The prediction of the depth of fracturing in the sides of underground excavations in coal seams is needed to determine the requirements for rib support and to assess pillar stability. The prediction requires consideration of how coal strength is determined and extrapolated to the mine scale and how stresses are redistributed around excavations in bedded coal masses. The impact of bedding in a stress analysis can be examined by adopting transverse isotropy and this results in much lower confining stresses in the horizontal plane and much higher vertical stresses close to the excavation boundary. The extent of rib scaling can be derived if the bedded coal is modelled as a brittle material. For coal pillars, the depth of scaling may be sufficient to have a material impact on their effective width and hence stability. The specification of rib support needs to consider how the failed coal may subsequently collapse.